Impact printer

ABSTRACT

An impact printer has hammer banks formed in a single plastic molding operation wherein hammer mounting flexures, hammer wear plates, magnet cores and shields are inserts in a single molding. Cooperating cantilevered snap in armatures are retained by elastomer pivot members and an adjustment bar carries individual adjustment screws which are locked against undesired rotation by a single wire element.

United States Patent [191 Charlson et al.

[111 3,811,377 [451 May 21, 1974 IMPACT PRINTER [75] Inventors: Paul Marlin Charlson; Karel den Tex, both of Rochester; Conrad Ferdinand Fingerson, Chatfield, all

of Minn.

[73] Assignee: International Business Machines Corporation, Armonk, NY. [22] Filed: Jan. 2, 1973 [21] Appl. No.: 320,249

[52] US. Cl 101/93 C [51] Int. Cl B4lf 9/06 [58] Field of Search 101/93 C, 93 R; 151/63 [56] References Cited UNITED STATES PATENTS 484,731 10/1892 Brown 151/63 3,172,352 3/1965 Helms 101/93 C 3,196,783 7/1965 Gross 101/93 C 3,282,203 11/1966 Kalbach et a1. 101/93 C 3,349,696 10/1967 Potter 101/93 C 3,447,455 6/1969 Shneider 101/93 C 3,556,002 l/197l Bragg 101/93 C 3,631,797 1/1972 Johnston et a1 101/93 C 3,635,156 l/l972 Krebs et al 101/93 C 3,636,865 l/1972 Konkel et a1 101/93 C 3,714,892 2/1973 Perry 101/93 C Primary Examiner-.1. Reed Fisher Assistant Examiner-William Pieprz I Attorney, Agent, or Firm-R0bert W. Lahtinen [5 7] ABSTRACT An impact printer has hammer banks formed in a single plastic molding operation wherein hammer mounting flexures, hammer wear plates, magnet cores and shields are inserts in a single molding. Cooperating cantilevered snap in armatures are retained by elastomer pivot members and an adjustment bar carries individual adjustment screws which are locked against undesired rotation by a single wire element.

7 Claims, 9 Drawing Figures FATENTEB m 2 m4 SHEET 2 [IF 3 FIG. 2

58 f A l FIG. 3'

PATENTEDHAY 21 1974 SHEEI 3 BF 3 FIG. 50 25 FIG. 8

IMPACT PRINTER BACKGROUND OF THE INVENTION The present invention is related to printers and more particularly to high speed, on-the-fly, impact printers using minimum dwell time.

Many common impact printing devices require as many as four or more column spaces to accommodate a print hammer assembly. Such devices require multi level stacking of the actuating mechanisms using push rods or equivalent devices to transmit motion and the accompanying power requirements entail the provision of significant power supply apparatus.

In the present invention, two hammer bank assemblies are opposed with the hammers interleaved and positioned along a single print line. The hammers are flexure mounted to a hammer assembly body with the entire hammer bank assembly molded as a single unit with a plastic matrix. This molding includes fiber reinforced composite or other material as a flexure material insert to provide a final flexure that has the ability to withstand the flexing in the printer environment and also imparts a biasing force to restore and retain the hammer in an inoperative, at rest position. The hammer formed of impact plastic is provided with a metal wear surface which is also made a unitary part of the molding by insertion into the mold cavity to thereafter become a captive portion of the molded part during the molding cycle.

In addition, in the illustrated embodiment the magnet cores and shield between adjacent magnet assemblies are formed as a part of the plastic molding by insertion into the mold cavity as inserts.

The actuating armatures on each hammer assembly are detented by an elastomer tube about the axis of which pivoting motion nominally occurs. The elastomer tube provides extended life, toughness, elasticity, and desired damping. This retention structure provides more consistant armature action due to the lack of play found in a rigid metal pivot pin pivot, experiences less wear and affords simplified fabrication, assembly and maintenance.

Hammer adjustments can be effected individually by respectively associated adjustment screws that are locked against undesired rotation by a single wire element that intersects the path of each adjustment screw.

It is an object of this invention to provide a simplified unitary, single-part flexure mounted hammer assembly that is easily adjusted and adapted to print on minimal center to center distances. It is also an object to provide a printer with an easily fabricated, snap in, cantilevered armature, that is detented in position by an elastomer member which also afiords a damping action. It is another object to provide hammer assemblies with a simplified structure. These and other objects and advantages of the invention will be apparent from the following particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I shows an isometric view of a single hammer bank of the present invention with the adjustment bar partially broken away. the cooperating type wheel schematically illustrated and partially in phantom view and a coil and bobbin assembly exploded from the assembled position. FIG. 2 is a plan view of the printer of the present invention showing the opposed hammer assemblies. FIG. 3 is a front elevation of the printer of FIG. 2. FIG. 4 is an enlarged partial elevation view of the shield, armature end portion and elastomer tub-e retainer. FIG. 5 is a perspective view of the fiber reinforced preform used for molding the fiexures of the hammer assembly. FIG. 5A is a vertical section of one side of the preform of FIG. 5. FIG. 6 is an enlarged isometric view of a lower print hammer portion. FIG. 7 is an enlarged isometric view of a portion of the metal strip used as a mold insert. FIG. 8 is an isometric view partially expolded of the adjustment bar.

DETAILED DESCRIPTION Referring to FIGS. 1, 2 and 3 a rear strike impact printer is shown having a pair of print hammer assemblies l0 and 11 with the hammer elements interleaved to form a common print line in cooperation with a print wheel 12.

Each of the print hammer assemblies 10 and II is formed as a unitary structure by including the cores '14, the shield 15, flexure l6 and hammer wear plates 18 as inserts in a molding using an impact resistant thermoset matrix material. The hammers 20 and flexures l6 for each assembly are. formed as a single unit in the molding process and thereafter separated into individual flexure mounted hammers 20 by grinding away the material therebetween. The fiexures 16 are formed by using a pair of inserts 22 as shown in FIG. 5, which have continuous aligned fibers 23 oriented as shown in FIG. 5a and a matrix of partially cured plastic material. The reinforcing fibers are accordingly, longitudinally aligned in the finally formed flexure elements of the hammer assembly. The insert 22 of FIG. 5 is formed with continuous aligned glass fibers 23 in a partially cured epoxy matrix to positively retain the unidirectional fiber alignment and in the fully cured state, following the molding of the assembly, to maintain uniform hammer height. The flexure preform is molded with a bead 25at each side which assures mechanical locking at each end of the flexure in the final print hammer molded assembly.

The steel wear plate 18 on the face of each hammer 20 is provided by a single insert strip which extends the length of the assembly and is thereafter parted by a grinding operation as are the hammers and flex ures. The metallurgical bond between the hammer faced material and plastic matrix of the hammer is not sufficient to withstand the shock of print hammer operation. It is therefore necessary to also establish a mechanical bond. The wear plate strip 27 is prepared as illustrated in FIG. 7 by copper plating the upper surface and thereafter sintering a layer of powdered particles 28 onto the surface. The copper plating along the interface serves to braze the particles to the iron strip. The iron particles project and present re-entrant surfaces which effect a mechanically locked joint when the plastic matrix material flows around such particles during the molding cycle.

The shields 15; which provide isolation between adjoining magnet positions to avoid crosstalk, provide a path for heat dissipation to protect the coils and each have a U-shaped cutout 29 to create a tab 30 that effects coil retention in an assembled condition; are also formed as integral part of the basic hammer assembly molding by inclusion as mold inserts. The E-cores 14 for the magnets associated with each hammer position are also held captive as inserts in the hammer assembly molding. A core 14 is shown in phantom view in the front elevation of FIG. 3. In FIGS. 1 and 2, the cores I4 underlie the armatures 40 respectively at each hammer position and are obscured from view.

The hammer assembly molding is formed by placing the inserts in the mold, that is the shields 15, cores l4, continuous flexure material inserts 22, and the continuous wear plate strip 27 that ultimately provides wear plates 18. The part is then formed and the plastic material cured. The matrix material cures as does the partially cured matrix of the continuous flexure inserts 22. As molded, the flexure elements 22 incline upwardly from the horizontal hammer element so that in the final assembled condition, an upward biasing force is exerted on the hammers 20, as the latter is maintained slightly depressed to effect a restoring action following hammer deflection during a print cycle. The molded flexure mounted hammer is designed in such manher that although the path of hammer travel during a print cycle is arcuate, the direction of hammer travel at the time of impact with the document is perpendicular to the document and in a radial direction with respect to the character wheel 12. When the completed molded part is removed from the mold, the hammer wear plate strip is selectively ground away to remove all but the width of metal facing coextensive with the width of the hammer portion 32 as seen in FIG. 6. The forming of the hammer face from a continuous piece of 7 material following the molding of the assembly enables the hammer to be correctly formed and properly aligned thereby overcoming any problems that might arise during the molding operation such as shrinkage. As a result of the molding operation, in addition tothe continuous flexures, adjoining hammers are joined by webs 34 of matrix material. A second grinding operation removes the webs 34 of matrix material and portions of the continuous flexures 22 to form an individual hammer at each position, supported by a pair of flexures l6 coextensive in width with such hammers.

A series of coils 36, one of which is shown removed from an assembled condition in FIG. 1, are positioned about the center elements of each E-core 14. A thin wall bobbin'has an upper projecting portion 37 which supports the terminals 38. The projecting portions 37 extend, in the assembled condition, between an armature 40 and the adjoining shield 15 to present the terminals above the surface defined by the top surfaces of shields 15. The terminals for the assembly are received by a plug 42 insuring a unique keyed connection. The coils are retained about the core element by the detent tab on the adjoining shield 15.

As seen in FIGS. 3 and 4, shields 15 are provided with a re-entrant curved surface 44 having a circular portion and an opening 45 which is smaller than the diameter of the circular portion. An elastomer tube 46 of slightly larger diameter than the diameters of the shield curved surfaces 44, extends the lengthof the assembly and is retained by mechanically locked elastic detenting contact within shield surfaces 44. An armature is installed at each hammer position by sliding the armature end 48 under the elastomer tube 46 whereupon tube 46 engages detent surface 49 to effect retention. By pivoting the armature 40 at one end and engaging the hammer 20 at the opposite end, motion magnification is obtained using the strongest element of the assembly. The opposite end of each armature 40 is interposed between an adjustment screw 50 that forms an upstop and the print hammer 20 at that print position. The molded matrix projections 41 adjoining shields 15 provide guidance for the adjoining armature 40 during vertical motion. Other projecting portions 43 (FIG. 4) of matrix material molded adjacent shields 15 at the opposite side of the cores 14 serve merely to center the adjacent armature 40 in alignment of the cooperating core. The biasing force exerted by the flexure l6 urges both hammer 20 and armature end 52 to the limit of upward travel defined by the position of adjustment screw 50.

An adjustment bar 54 is attached to printer frame 55 by bolts 56 and receives an adjustment screw 50 in overlying relation to each print hammer for limiting upward travel of such print hammer and the associated armature 40. Adjustment bar 54 includes a body portion 58 and an insert 59 that is received in the body portion channel 60 and secured by a means not shown. Cooperating channel 61 in the body portion channel 60 and insert 59 receive a wire which overlies a portion of each of the aligned bores 63 which respectively receive adjustment screws 50. Asthe screws 50 are inserted,

'interference between the .wire and the adjustment screw causes a locking, interference action which resists rotation of the adjustment screw. Interference between the wire and screws alternately disposed at opposite sides thereabove causes the wire to adopt a serpentine configuration through its active length. In an alternative embodiment the locking wire may be used with unthreaded bores 63 in the adjustment bar 59 and body 58 whereby the wire provides both a self threading driving engagement and a locking resistance to undesired screw rotation.

Underlying the print hammer assembly is a bed plate 65 which defines a transport path for a document 66 that is to pass the print station. Exposed to the docu' ment path through apertures in bed plate 65 is a print wheel 12 which presents a sequence of embossed characters at each print hammer position along the print line. The print wheel 12 is driven by belt 67. A quick change, long life ink roll 70 rotates in contact with print wheel 12 to provide an ink film on the print wheel characters for transfer to the document during print cycle. Ink roll 70 idles on a pivot 71 in housing 72. The housing 72 is pivotally mounted on printer frame 55 about pin 73 and is retained in a position to maintain contact between ink roll 70 and print wheels 12 by leaf spring latch 75 which retains housing projection 76. A pair of emitter pickups 79 and 80 sense the passage of teeth on emitter wheels which rotate in unison with the character wheel 12 to provide information as to when a character will be positioned at the print station for a print operation.

In operation, at a time when it is determined that actuation will cause a print operation when the selected character is present at the print station, the desired coil 36 is energized causing the associated armature 20 to seal-against core 14 imparting a power stroke to hammer 20. After the armature seals against the core, the hammer continues its downward motion against the upward biasing force of flexures 16, striking and delivering the document 66 into contact with the character wheel character present at the print station. Following brief contact during the rear strike print operation, the hammer rebounds, which energy combined with the upward biasing force of flexures l6 restores both hammer 20 and annature 40 to the position of rest in contact with upstop adjustment screw 50. In a typical environment, the preloaded hammer has a 0.015 inch power stroke followed by a 0.010 inch free flight. The coil pulse occurs for a 0.6 millisecond duration inducing a 075 millisecond flight time which results in a 0.0l millisecond contact time between the document and the type character traveling at 230' inches per second.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

l. A print hammer assembly comprising a plastic matrix body;

a plurality of elongated print hammers each carried by a pair of substantially parallel leaf spring elements extending from said body member;

a plurality of magnetic core elements carried by said body and respectively aligned with said plurality of print hammers;

a plurality of elongated armatures each respectively aligned with one of said print hammers and one of said core elements,

said armatures each having a detent adjacent one end and engaging said aligned print hammer adjacent the end opposite said one end; and

a cylindrical elastomer retaining member carried by said body and received in said armature detents, said armature detents being pivotally mounted about said elastomer retaining meber so as to restrict longitudinal movement of said armatures and to permit said armatures to pivot about an elastic pivot point for providing a damping action, whereby optimum magnetic coupling may be achieved between said armatures and the aligned magnetic cores. 2. The print hammer assembly of claim 1 further comprising a plurality of magnetic metal shield elements positioned at each axial side of each core element and molded as a unitary portion of said body, and aligned cylindrical openings in said shield elements in which said elastomer retaining member is received and retained. 3. The print hammer assembly of claim 2 wherein said elastomer retaining member is a tubular element having an outside diameter slightly in excess of the diameter of said aligned shield elements cylindrical openings,

whereby said elastomer retaining member is retained by constriction within said shield elements cylindrical openings.

4. The print hammer assembly of claim 2 wherein said armature presents a reduced height inclined surface at said one end whereby said armature may be manually inserted and withdrawn from said assembled condition with said elastomer retaining member,

5. The print hammer assembly of claim 4 further comprising a stop member confronting a plurality of armatures at a side opposite said plurality of print hammers and wherein said leaf spring elements are preloaded in a non-printing direction,

whereby said plurality of armatures are normally retained in abutting relation with said stop member and are restored to said abutting relation following a print cycle.

6. A print hammer assembly comprising a body member;

a plurality of elongated armatures each having a detent formed at one end;

a plurality of print hammers respectively aligned with said armatures adjacent the end opposite said one end;

means biasing said print hammers in a non-printing direction toward an abutting relation with said armatures at a side opposite that in which said detent is formed;

a plurality of electromagnetic actuator means carried by said body and respectively confronting said plurality of armatures intermediate said ends and at the same side as said plurality of print hammers;

stop means limiting travel of said plurality of armatures in said non-printing direction; and

a cylindrical elastomer retaining member carried by said body and received in said armature detents, said armature detents being pivotally mounted about said elastomer retaining member so as to restrict longitudinal movement of said armature and to permit said armatures to pivot about an elastic pivot point for providing a damping action.

7. The print hammer assembly of claim 6 wherein said body is formed of a matrix of molded plastic mate'- rial and further comprising a plurality of magnetic shield elements molded as inserts in said body material and disposed at each side of each electromagnetic actuating member to magnetically isolate adjoining actuating members, said shield elements having aligned cylindrical openings wherein said elastomer retaining member is received and retained. 

1. A print hammer assembly comprising a plastic matrix body; a plurality of elongated print hammers each carried by a pair of substantially parallel leaf spring elements extending frOm said body member; a plurality of magnetic core elements carried by said body and respectively aligned with said plurality of print hammers; a plurality of elongated armatures each respectively aligned with one of said print hammers and one of said core elements, said armatures each having a detent adjacent one end and engaging said aligned print hammer adjacent the end opposite said one end; and a cylindrical elastomer retaining member carried by said body and received in said armature detents, said armature detents being pivotally mounted about said elastomer retaining meber so as to restrict longitudinal movement of said armatures and to permit said armatures to pivot about an elastic pivot point for providing a damping action, whereby optimum magnetic coupling may be achieved between said armatures and the aligned magnetic cores.
 2. The print hammer assembly of claim 1 further comprising a plurality of magnetic metal shield elements positioned at each axial side of each core element and molded as a unitary portion of said body, and aligned cylindrical openings in said shield elements in which said elastomer retaining member is received and retained.
 3. The print hammer assembly of claim 2 wherein said elastomer retaining member is a tubular element having an outside diameter slightly in excess of the diameter of said aligned shield elements cylindrical openings, whereby said elastomer retaining member is retained by constriction within said shield elements cylindrical openings.
 4. The print hammer assembly of claim 2 wherein said armature presents a reduced height inclined surface at said one end whereby said armature may be manually inserted and withdrawn from said assembled condition with said elastomer retaining member.
 5. The print hammer assembly of claim 4 further comprising a stop member confronting a plurality of armatures at a side opposite said plurality of print hammers and wherein said leaf spring elements are pre-loaded in a non-printing direction, whereby said plurality of armatures are normally retained in abutting relation with said stop member and are restored to said abutting relation following a print cycle.
 6. A print hammer assembly comprising a body member; a plurality of elongated armatures each having a detent formed at one end; a plurality of print hammers respectively aligned with said armatures adjacent the end opposite said one end; means biasing said print hammers in a non-printing direction toward an abutting relation with said armatures at a side opposite that in which said detent is formed; a plurality of electromagnetic actuator means carried by said body and respectively confronting said plurality of armatures intermediate said ends and at the same side as said plurality of print hammers; stop means limiting travel of said plurality of armatures in said non-printing direction; and a cylindrical elastomer retaining member carried by said body and received in said armature detents, said armature detents being pivotally mounted about said elastomer retaining member so as to restrict longitudinal movement of said armature and to permit said armatures to pivot about an elastic pivot point for providing a damping action.
 7. The print hammer assembly of claim 6 wherein said body is formed of a matrix of molded plastic material and further comprising a plurality of magnetic shield elements molded as inserts in said body material and disposed at each side of each electromagnetic actuating member to magnetically isolate adjoining actuating members, said shield elements having aligned cylindrical openings wherein said elastomer retaining member is received and retained. 